Feeding- spitting up

Hey so my baby is 17 days and I’ve been feeding her formula and breastfeeding on and off but at night I do my best to breast feed all night.. but the last few days she’s been spitting up and choking and I can’t go to sleep comfortably when she naps because she chokes so silently and when I least expect it she has milk running out her mouth and nose as she chokes... any reason for this or tips???